Uranium-238 has a half-life of about 5 billion years, which is approximately the age of the Earth. Uranium-235 has a half life of about years, about one-seventh as long as the half life of uranium-238.
(11) How many uranium-238 atoms remain in terms of the original number x?
The question involves the use of the equation describing half-life decay:
In this case, one half-life of uranium-238 has passed.